Honda Shadow Forums banner

1 - 8 of 8 Posts

·
Registered
Joined
·
79 Posts
Discussion Starter #1
As I replaced some spark plugs I noticed the previous owner used the "7" and not the "8".

A 7 plug is designed for cold climates. I was surprised to find them in the bike. The Clymer mentions them in the respect they are used to fix some engine issues.

What does this plug do in the engine? Run hotter? cooler? why use them here?

Thanks
 

·
Registered
Joined
·
190 Posts
I don't think the heat range of a plug has anything to do with ambient temperature, only the insulator tip temperature (heat range).

In days of old when I was working on 2-strokes at a dealership, guys that were running NGK-B8ES plugs for example, and having plug fouling problems (usually from worn rings), they would switch to the hotter B7ES plug to keep the fuel mixture burned off the insulator and electrode until they got around to rebuilding the top end, and then would go back to the recommended heat range. (Switching to a B6-ES in the above example would probably guarantee a hole in the piston, especially if run a lot at high rpm.)

I don't recall ever hearing seasonal temperature being a reason for changing plug heat range. In some cases, running a hotter heat range can cause detonation, and in extreme cases, can burn a hole in the piston. If you think about it, the difference between say 10 degrees in the winter and 100 degree weather in the summertime, is a pretty small percentage change compared to the temperature that the plug is subjected to inside the combustion chamber, so ambient temperature probably would have little effect on the plug tip temp. If it were me, I'd stick with the heat range recommended in the "book" unless you run consistently at very high rpm, then you might could consider one range cooler.

Rick
 

·
Registered
Joined
·
3,761 Posts
tropicalsuns said:
As I replaced some spark plugs I noticed the previous owner used the "7" and not the "8".

A 7 plug is designed for cold climates. I was surprised to find them in the bike. The Clymer mentions them in the respect they are used to fix some engine issues.

What does this plug do in the engine? Run hotter? cooler? why use them here?

Thanks
The term "hot plug" and "cold plug" are kind of mis-leading.

The spark plug has a job to help remove heat from the cylinder.
The amount of heat that it removes is in relation to it's "heat range".
What is really confusing to a lot of people is that a "cold plug" removes
MORE heat from the cylinder and a "hot plug" removes less heat.

A cold plug is better used in high performance applications and high temperature applications.
In high ambient heat, gasoline tends to detonate (ping) and going to a
colder plug will remove more heat from the combustion chamber and
assist in reducing detonation.

A 'hotter plug' is generally used in extreme cold condition to help keep
the cylinder temperature up.
Some people will also use hotter plugs in engines that use oil.
In engines that use oil, a hotter plug will help keep fouling down
due to the oil being burned in the combustion chamber.
It's not a fix, but a band-aid for people who don't want to fix it correctly.

Japanese spark plugs are heat ranged rated the exact opposite of
American plugs. A heat range of 7 is a hotter plug than an 8 or 9.
As the numbers go up, on a Japanese plug, the colder the plug is.
Being in NV, I don't know why the previous owner would have gone
to a hotter plug, unless they just didn't know any better.
I'd recommend putting the 8's back in it and unless you notice pinging or
other drivability problems, stick with them. If you get a little pinging,
they you might want to go up to a 9... or if you do a lot of high speed
riding, you might want to go up to a 9. Otherwise, just put the 8's in there.
 

·
Registered
Joined
·
190 Posts
litnin,

It's been a while so I may not remember correctly, but aren't Nippon (ND) plug heat ranges backwards from NGK, i.e. an NGK 6 is hotter than a 7, and an ND 7 is hotter than a 6?

Edit (Never mind, just answered my own question ... larger is colder for both)
 

·
Registered
Joined
·
3,761 Posts
Kermitdafrog said:
litnin,

It's been a while so I may not remember correctly, but aren't Nippon (ND) plug heat ranges backwards from NGK, i.e. an NGK 6 is hotter than a 7, and an ND 7 is hotter than a 6?

Edit (Never mind, just answered my own question ... larger is colder for both)
Nope, the higher the number on both, the colder the plug.
However, a Nippon Denso 8 is not equivalent to a NGK 8.
The heat range number does not signify the same amount
of heat dissipation.
 

·
Registered
Joined
·
134 Posts
Acording to the Owners manual for my bike (1999 Ace 750)
It states to use the colder plug range (2 are listed) durring sustained high speed operation, and/or high ambient temps. I have never changed the plugs on mine but that is what is listed. A hotter plug will also tend to burn cleaner if there is an oil blow by problem or something of that nature.
 

·
Registered
Joined
·
190 Posts
However, a Nippon Denso 8 is not equivalent to a NGK 8.
Yeah, until I looked it up, I couldn't remember what any of the ND two-digit heatrange numbers were for NGK heatrange equivalents, so was using the single digit numbers as an example.

Here is a site that has some pretty good plug info with some "plug reading" examples:

http://home.alltel.net/jfarrell/NGKSparkPlugInformation.html

Rick
 
1 - 8 of 8 Posts
Top